Magnetic field detector

The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Naval Information Warfare Center Pacific, Code 72120, San Diego, CA, 92152; (619) 553-5118; NIWC_Pacific_T2@us.navy.mil. Reference Navy Case Number 111478.

Magnetic field detectors are devices that sense magnetic fields or magnetic dipole moments. One example of a magnetic field detector is a Superconducting Quantum Interference Device (SQUID), which are one of the highest sensitivity types of magnetic field detectors. SQUIDs utilize a small loop of superconducting material with two weak links called Josephson Junctions (JJs) to sense the magnetic field. A SQUID array consists of a single circuit of many SQUID elements that are arranged in one, two, or three spatial dimensions. When a SQUID array consists of a non-linear distribution of SQUID elements, the circuit exhibits a voltage-flux transfer function with a single minimum, called the anti-peak, under an applied local magnetic field. SQUIDs have many uses, such as in magnetic property measurement systems (e.g., SQUID magnetometry), magnetic anomaly detectors, magnetic resonance imaging, or scanning SQUID microscopy.

A SQUID is a superconductor material loop containing at least one Josephson junction, which allows for the measurement of magnetic flux quanta when a magnetic field threads the superconducting loop. A SQUID array is a single superconducting circuit comprised of many (e.g., 10 to 1 million) individual SQUID elements that are connected in one, two, or three-dimensional configurations. In general, the temperature-dependent direct current (DC) and alternating current (AC) response of a SQUID or SQUID array depends on the superconductor material used to fabricate the SQUID elements, the tunnel barrier material which comprises the Josephson Junction (commonly an insulator), and the geometry configuration of the superconducting circuit (e.g. trace volume, loop area, tunnel barrier volume, etc.). Currently, a new SQUID or SQUID array has to be fabricated to adjust or optimize the DC and RF performance metrics for each application the SQUID or SQUID array is being used for or each platform the SQUID or SQUID array is being used in. Therefore, the fabrication of a new SQUID or SQUID array for each new application or a change in an existing application can result in a significant investment of time and resources.

A magnetic field detector is disclosed herein that is used for detecting direct current and alternating current magnetic fields. The magnetic field detector has one or more heater elements that are used on one or more SQUID elements. The heater elements contact all the tunnel barriers of the Josephson junctions on each SQUID element. The heater elements are also connected to a tunable power source. The tunable power source provides impedance tuning to the SQUID elements via the heater elements by tuning the power, which can adjust the temperature of the SQUID elements through the heater elements. Adjusting the local temperature reduces or eliminates mismatch losses that result from interfacing different circuits or electronics operating at different temperatures. In addition, the direct current (DC) and alternating current (AC) response of the SQUID elements can be tuned, which results in a higher sensitivity magnetic field sensor. As a result of the ability to tune the impedance, DC, or AC response, post-fabrication imperfections can be corrected without a need to fabricate a new magnetic field detector or repair the magnetic field detector. In addition, a new magnetic field detector does not need to be fabricated to adjust or optimize the DC and RF performance metrics for each application the magnetic field detector is being used for or each platform the magnetic field detector is being used in.

The magnetic field detector herein includes a substrate, two or more Josephson junctions, and one or more heater elements. The two or more of Josephson junctions are connected to each other by superconducting interconnected paths via a superconducting material and are arranged in an array. The one or more heater elements directly or indirectly adjust the temperature of at least one Josephson junction via a tunable power source.

Referring now to, a top view and side view, respectively, of an example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown. The patterning inis for illustrative purposes only to aid in viewing and should not be construed as being limiting or directed to a particular material or materials.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this particular example, the heater elementdirectly contacts each tunneling barrierof each Josephson junctionby contacting a top portion of the tunneling barrier. The heating elementcontacts each tunneling barrierby bisecting each Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together. Each component of the SQUID element with asymmetric Josephson junctionsis discussed in detail below.

The substratemay be any known substratethat is used to synthesize thin-film or bulk superconductor materials. Some examples of the substrate material include crystalline materials, amorphous materials, or polycrystalline materials. Some specific examples of the substrate include MgO, SrTiO, CaF, LaAlO, AlO, SrF, BaF, ZrO, Si, or combinations thereof.

The superconducting materialaffects the temperature-dependent direct current (DC) and alternating current (AC) response of a SQUID element or SQUID array in the magnetic field detector. Some examples of the superconducting materialinclude any low or high temperature superconducting material, such as a metal or metal alloy. Some examples include Nb, Al, YBCO, NbTi, NbN, NbGe, NbAl, NbCN, NbSn, and combinations thereof. The superconducting materialis the same material as the superconducting interconnecting paths(discussed in detail below).

The two or more Josephson junctionsare connected to each other by superconducting interconnecting pathswhere the two or more Josephson junctionsare arranged in an array. The two or more Josephson junctionsare organized into superconducting interference devices (SQUIDs) where each SQUID comprises two Josephson junctions connected to each other by the superconducting interconnecting path. Each Josephson junctionis positioned on the superconducting materialalong the superconducting interconnected path. In the example in, the Josephson junctionseach include the tunneling barrierand a portion of the heating elementthat directly or indirectly contacts the tunneling barrier, which is shown by the dashed line rectangles. In the example in, the Josephson junctionsare centrally located on the superconducting material. In other examples, the Josephson junctionsmay be located anywhere on the superconducting materialas long as the two Josephson junctionsare aligned and opposite each other for a heating elementto directly or indirectly contact both Josephson junctions.

The two or more Josephson junctionsform an array of Josephson Junctions when connected together. Some examples of an array of Josephson Junctions are at least three Josephson junctions connected in one, two, or three-dimensions. For example, a one-dimensional array includes two or more Josephson junctions connected in-series or parallel. A two-dimensional array includes two or more Josephson junctions connected in-series and parallel along an X-axis and Y-axis direction. A three-dimensional array could entail two or more Josephson junctions connected in-series, parallel, and stacked together in the Z-direction with other Josephson junctions connected in-series and parallel. Any type of one, two, or three-dimensional array may be used to connect the two or more Josephson junctions. Therefore, the magnetic field detector may have any number of Josephson junctionsarranged in any type of configuration.

In particular, the two or more Josephson junctionsmay have symmetrical Josephson junctions, asymmetrical Josephson junctions, or a combination of both symmetrical and asymmetrical Josephson junctions. For example, the two or more Josephson junctions may have a width ranging from about 5 nanometers to about 100 micrometers. In an example, the width may vary within the array of Josephson junctions, as shown inwhen the width is asymmetrical. When the width varies within the array of the two or more Josephson junctions, the width variation is equal to or less than 40% within the array. For example, if the largest Josephson junction width is about 1 micrometer, the smallest Josephson junction width is about 0.6 micrometer. In another example, the width is the same for the two or more Josephson junctionswithin the array, when the width of the Josephson Junctions are symmetrical.

In another example, the two or more Josephson junctionsare organized into bi-superconducting quantum interference device (bi-SQUIDs). Each bi-SQUID includes two Josephson junctionsin a superconducting loop and a third Josephson junctionin a superconducting path that bisects the superconducting loop. At least one superconducting interconnecting path, that connects any two Josephson junctions, exhibits a volume-geometry difference relative to the remaining superconducting interconnecting pathsthat connect remaining Josephson junctionsin an array. In other words, by modifying the thickness of the superconductor interconnecting material, the bi-SQUIDs can have asymmetric or symmetric Josephson junctions.

Similar to the superconducting material, the superconducting interconnecting pathsmay be made of any low or high temperature superconducting material, such as a metal or metal alloy. Some examples include Nb, Al, YBCO, NbTi, NbN, NbGe, NbAl, NbCN, NbSn, and combinations thereof. When the magnetic field detectorincludes an array of Josephson junctions, the superconducting interconnecting pathsform a three-dimensional grid array. The three-dimensional grid array of the superconducting interconnecting pathscan be arranged uniformly or non-uniformly.

Referring back to, the SQUID element with asymmetric Josephson junctionsfurther includes one or more heater elements. The one or more heater elementsdirectly or indirectly adjusts the temperature of at least one Josephson junctionvia a tunable power source. The tunable power source may be any tunable power source that can provide sufficient power to adjust the temperature of the magnetic field detector. The one or more heater elementsmay be made of a metallic material, semi-metallic material, or a combination thereof. The one or more heater elementsmay also be different shapes, such as a straight strip line, a meander strip line, or a combination thereof. In the example shown in, the heater elementis a straight strip line that directly contacts the top portion of the tunneling barrierof each Josephson junctions. In, an example of a heating elementwith a meander strip line that directly contacts the top portion of the tunneling barrierof each Josephson junctions. Additional examples of the one or more heater elementsare discussed in.have patterning for illustrative purposes only to aid in viewing and should not be construed as being limiting or directed to a particular material or materials. In addition, the examples ininclude all of the components are the same components as previously described herein for.

Referring now to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. However, in this example, the heater elementdirectly contacts a side portion of the tunneling barrierby extending parallel to the tunneling barrier. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. This example includes the heater elementdirectly contacting the tunneling barrierof at least one Josephson junctionas a straight strip line by extending through the tunneling barrierand bisecting each Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now toa top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this particular example, the heater elementdirectly contacts each tunneling barrierof at least one Josephson junctionas a straight strip line by contacting a top portion of the tunneling barrier. In this example, there are two heater elementswhere the two heater elementsare small strip line fragments centered on each tunneling barrier. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, there are two heater elementswhere the two heater elementsare small strip line fragments centered on each side portion of the tunneling barrier. The heater elementdirectly contact the tunneling barrierof at least one Josephson junctionon each side by attaching the heater elementto the outer side of the tunneling barrierof each Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring not to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, the heater elementis embedded in a nonmagnetic, non-electrically conductive material. The nonmagnetic, non-electrically conductive materialis between the substrateand the superconducting material, Josephson junctions, and superconducting interconnecting paths. As a result, in this example, the heater elementdirectly contacts the bottom portion of the tunneling barrieras a straight strip line of at least one Josephson junctionby extending through the nonmagnetic materialto bisect each Josephson junctionand the nonmagnetic material. In other examples, the heater elementcan indirectly contact the tunneling barrierof at least one Josephson junctionif the heater elementwas embedded in a portion of the nonmagnetic, non-electrically conductive materialthat does not contact the tunneling barrierof either Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view, a side view, and a cross-sectional view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, the heater elementis embedded in a nonmagnetic, non-electrically conductive materialas a straight strip line. However, in, the nonmagnetic, non-electrically conductive materialis on top of the superconducting material, Josephson junctions, and superconducting interconnecting paths. As a result, in this example, the heater elementdirectly contacts the top portion of the tunneling barrierof at least one Josephson junctionby extending through the nonmagnetic, non-electrically conductive materialto bisect each Josephson junctionand the nonmagnetic, non-electrically conductive material. In other examples, the heater elementcan indirectly contact the tunneling barrierof at least one Josephson junctionif the heater elementwas embedded in a portion of the nonmagnetic, non-electrically conductive materialthat does not contact the tunneling barrierof either Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, the heater elementis attached to the top portion of a nonmagnetic, non-electrically conductive material. The nonmagnetic, non-electrically conductive materialembeds the superconducting material, Josephson junctions, and superconducting interconnecting pathsas shown in. As a result, the heater elementindirectly contacts the tunneling barrierof at least one Josephson junctionthrough the nonmagnetic, non-electrically conductive material. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, the heater elementis embedded in a nonmagnetic, non-electrically conductive material. However, in, the nonmagnetic, non-electrically conductive materialis between the superconducting material, Josephson junctions, and superconducting interconnecting pathsand the substrate. As a result, in this example, the heater elementdirectly contacts the bottom portion of the tunneling barrierof at least one Josephson junctionby extending through the nonmagnetic, non-electrically conductive materialto bisect each Josephson junctionand the nonmagnetic, non-electrically conductive material. In other examples, the heater elementcan indirectly contact the tunneling barrierof at least one Josephson junctionif the heater elementwas embedded in a portion of the nonmagnetic, non-electrically conductive materialthat does not contact the tunneling barrierof either Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view and side view, respectively, of another example of a SQUID element with asymmetric Josephson junctionsused in a magnetic field detector is shown.show an example of the SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas two asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In this example, the heater elementis on top of and embedded in a nonmagnetic, non-electrically conductive material. In, the nonmagnetic, non-electrically conductive materialis on top of the superconducting material, Josephson junctions, and superconducting interconnecting paths. As a result, in this example, the heater elementdirectly contacts the top portion of the tunneling barrierof at least one Josephson junctionby extending above and into the nonmagnetic, non-electrically conductive material. In other examples, the heater elementcan indirectly contact the tunneling barrierof at least one Josephson junctionif the heater elementextends into a portion of the nonmagnetic, non-electrically conductive materialthat does not contact the tunneling barrierof either Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

Referring now to, a top view, a side view, and a top view of another example, respectively, of a bi-SQUID element with asymmetric Josephson junctions used in a magnetic field detector is shown.show an example of the bi-SQUID element with asymmetric Josephson junctionsthat includes the substratewith a superconducting materialattached to the substrate. In this example, the superconducting materialhas three asymmetric Josephson junctions. Each Josephson Junctionhas a tunneling barrier. In the example shown inand, the heater elementdirectly contacts the top portion of the tunneling barrierof each Josephson junctionthe heater elementpasses over. In the example shown in, there are two heater elementswhere one heater elementdirectly contacts the top portion of the tunneling barrierof two Josephson junctionsand the second heater elementdirectly contacts the top portion of the tunneling barrierof an individual Josephson junction. The SQUID element with asymmetric Josephson junctionsalso includes two superconducting interconnecting pathson each side of the superconducting materialthat connect each SQUID element together.

A superconducting quantum interference system is also disclosed herein. The superconducting quantum interference system includes a substrate, a grid of superconducting interconnecting paths, a plurality of superconducting quantum interference device (SQUIDs), and one or more heater elements. The substrate, the grid of superconducting interconnecting paths, the plurality of SQUIDs, and the one or more heater elements are the same substrate, the grid of superconducting interconnecting paths, the plurality of SQUIDs, and the one or more heater elements as previously described herein. The plurality of SQUIDs are arranged in a two-dimensional array on the grid of superconducting interconnecting paths. The superconducting interconnecting paths connect the plurality of SQUIDs to each other. The one or more heater elements include at least one section of the plurality of SQUIDS that have at least one individual heater element that directly or indirectly adjusts the temperature of at least one SQUID via a tunable power source. The individual heater elements adjust the temperature of the section of the plurality of SQUIDs via an independent and tunable power source.

As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of a list should be construed as a de facto equivalent of any other member of the same list merely based on their presentation in a common group without indications to the contrary.

Unless otherwise stated, any feature described herein can be combined with any aspect or any other feature described herein.

Reference throughout the specification to “one example”, “another example”, “an example”, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

In describing and claiming the examples disclosed herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.